A realized facilitation cascade mediated by biological soil crusts in a sagebrush steppe community.

Biological soil crusts can have strong effects on vascular plant communities which have been inferred from short-term germination and early establishment responses. However, biocrusts are often assumed to function as an "organizing principle" in communities because their effects can "cascade" to interactions among crust-associated plant species. We conducted surveys and experiments to explore these cascades and found that biocrusts were positively associated with large patches (> 10 m diameter) of a dominant shrub Artemisia tridentata. At the smaller scale of individual shrubs and the open matrices between shrubs, biocrusts were negatively associated with Artemisia. Juveniles of Artemisia were found only in biocrusts in intershrub spaces and never under shrubs or in soil without biocrusts. In two-year field experiments, biocrusts increased the growth of Festuca and the photosynthetic rates of Artemisia. Festuca planted under Artemisia were also at least twice as large as those planted in open sites without crusts or where Artemisia were removed. Thus, biocrusts can facilitate vascular plants over long time periods and can contribute to a "realized" cascade with nested negative and positive interactions for a range of species, but unusual among documented cascades in that it includes only autotrophs.

Volatile-Mediated Induced and Passively Acquired Resistance in Sagebrush (Artemisia tridentata).

Plants produce a diversity of secondary metabolites including volatile organic compounds. Some species show discrete variation in these volatile compounds such that individuals within a population can be grouped into distinct chemotypes. A few studies reported that volatile-mediated induced resistance is more effective between plants belonging to the same chemotype and that chemotypes are heritable. The authors concluded that the ability of plants to differentially respond to cues from related individuals that share the same chemotype is a form of kin recognition. These studies assumed plants were actively responding but did not test the mechanism of resistance. A similar result was possible through the passive adsorption and reemission of repellent or toxic VOCs by plants exposed to damage-induced plant volatiles (DIPVs). Here we conducted exposure experiments with five chemotypes of sagebrush in growth chambers; undamaged receiver plants were exposed to either filtered air or DIPVs from mechanically wounded branches. Receiver plants exposed to DIPVs experienced less herbivore damage, which was correlated with increased expression of genes involved in plant defense as well as increased emission of repellent VOCs. Plants belonging to two of the five chemotypes exhibited stronger resistance when exposed to DIPVs from plants of the same chemotypes compared to when DIPVs were from plants of a different chemotype. Moreover, some plants passively absorbed DIPVs and reemitted them, potentially conferring associational resistance. These findings support previous work demonstrating that sagebrush plants actively responded to alarm cues and that the strength of their response was dependent on the chemotypes of the plants involved. This study provides further support for kin recognition in plants but also identified volatile-mediated associational resistance as a passively acquired additional defense mechanism in sagebrush.

[Responses of spatial distribution pattern of the dominant population Artemisia ordosica to enclosure restoration in desert steppe.] / è’æ¼ è‰åŽŸä¼˜åŠ¿ç§ç¾¤æ²¹è’¿ç©ºé—´åˆ†å¸ƒæ ¼å±€å¯¹å°è‚²æ¢å¤çš„å“åº”.

Shrubs play an important role in maintaining biodiversity, stability and ecological service in grassland. Exploring the effects of enclosure on dominant shrub population can provide scientific guidance for grassland restoration and tending management. In this study, we investigated main growth characteristics and spatial distribution pattern of Artemisia ordosica population in four enclosed grasslands with duration of 0, 5, 15, and 25 years. The results showed that population density increased first and then decreased with time extension, and peaked after enclosed for 15 years, which was 3.7 times that of unenclosed plot. The crown and projected area showed opposite responses trend to that of density, which decreased by 31.7% and 52.3% after enclosed 15 years, respectively. The height decreased by 25.3% after 5 years of enclosure, and then increased gradually. Semi-variance function analysis showed that population distribution in all grasslands conformed to Gaussian model. The spatial variation decreased gradually in the early stage of enclosure, and then increased after enclosed for 15 years. Structure ratio in each plot was higher than 0.75, but nugget was relatively small, indicating that spatial autocorrelation of population was mainly affected by structural factors rather than random factors. Spatial distribution of A. ordosica population was patchy and striped. Enclosure reduced spatial variation of population at small scale. However, spatial heterogeneity and scale dependence of population enhanced after enclosed 25 years as plaque dissociating. Our findings suggest that enclosure duration is the key factor affecting plant growth and spatial distribution of dominant population in desert steppe. Long-term fencing enhances the spatial heterogeneity of dominant population. Appropriate human intervention should be carried out after 15 years of enclosure.

Allelopathic effect of Artemisia argyi on the germination and growth of various weeds.

Allelopathy means that one plant produces chemical substances to affect the growth and development of other plants. Usually, allelochemicals can stimulate or inhibit the germination and growth of plants, which have been considered as potential strategy for drug development of environmentally friendly biological herbicides. Obviously, the discovery of plant materials with extensive sources, low cost and markedly allelopathic effect will have far-reaching ecological impacts as the biological herbicide. At present, a large number of researches have already reported that certain plant-derived allelochemicals can inhibit weed growth. In this study, the allelopathic effect of Artemisia argyi was investigated via a series of laboratory experiments and field trial. Firstly, water-soluble extracts exhibited the strongest allelopathic inhibitory effects on various plants under incubator conditions, after the different extracts authenticated by UPLC-Q-TOF-MS. Then, the allelopathic effect of the A. argyi was systematacially evaluated on the seed germination and growth of Brassica pekinensis, Lactuca sativa, Oryza sativa, Portulaca oleracea, Oxalis corniculata and Setaria viridis in pot experiments, it suggested that the A. argyi could inhibit both dicotyledons and monocotyledons not only by seed germination but also by seedling growth. Furthermore, field trial showed that the A. argyi significantly inhibited the growth of weeds in Chrysanthemum morifolium field with no adverse effect on the growth of C. morifolium. At last, RNA-Seq analysis and key gene detection analysis indicated that A.argyi inhibited the germination and growth of weed via multi-targets and multi-paths while the inhibiting of chlorophyll synthesis of target plants was one of the key mechanisms. In summary, the A. argyi was confirmed as a potential raw material for the development of preventive herbicides against various weeds in this research. Importantly, this discovery maybe provide scientific evidence for the research and development of environmentally friendly herbicides in the future.

The effects of fire on the thermal environment of sagebrush communities.

Thermal heterogeneity provides options for organisms during extreme temperatures that can contribute to their fitness. Sagebrush (Artemisia spp.) communities exhibit vegetation heterogeneity that creates thermal variation at fine spatial scales. However, fire can change vegetation and thereby variation within the thermal environment of sagebrush communities. To describe spatial and temporal thermal variation of sagebrush communities following wildfire, we measured black bulb temperature (Tbb) at 144 random points dispersed within unburned and burned communities, for 24-h at each random point. We observed a wide thermal gradient in unburned (-7.3° to 63.3 °C) and burned (-4.6° to 64.8 °C) sagebrush communities. Moreover, unburned and burned sagebrush communities displayed high thermal heterogeneity relative to ambient temperature (Tair). Notably, Tbb varied by 47 °C in both unburned and burned communities when Tair was 20 °C. However, fire greatly reduced the buffering capacity and thermal refuge of Wyoming big sagebrush (A. tridentata wyomingensis) communities during low and high Tair. Furthermore, fire increased Tbb in Wyoming big sagebrush and mountain big sagebrush (A. t. vaseyana) during the mid-day hours. These results demonstrate how fire changes the thermal environment of big sagebrush communities and the importance of shrub structure which can provide thermal refuge for organisms in burned communities during extreme low and high Tair.

[Stoichiometric characteristics of Artemisia sacrorum communities under different site conditions and their correlation with soil nutrients]. / ä¸åŒç«‹åœ°é“æ†è’¿åŒ–å­¦è®¡é‡ç‰¹å¾åŠå ¶ä¸ŽåœŸå£¤å »åˆ†çš„å ³ç³».

We explored the stoichiometric characteristic of Artemisia sacrorum communities and its correlation with soil characters by considering the aspect and slope position, and variation of soil nutrient in Yangqingchuan catchment of Wuqi. Our results showed that total carbon, total nitrogen, total phosphorus contents and C:N ratio in A. sacrorum (both shoot and root) in the top of hillock>sunny slope>semi-shady slope>shady slope. The C:P ratio in shoot and the N:P ratio in root decreased consistently. The N:P ratio in shoot and the C:P ratio in root decreased first and then increased. While the total nitrogen and total phosphorus in shoot, and the organic carbon in root increased first and then decreased with the decreases of slope position, the C:N ratio and N:P ratio in shoot decreased first and then increased. The stoichiometric characteristic of A. sacrorum communities was positively correlated with the soil stoichiometric characteristics. However, the C:N ratio, C:P ratio and N:P ratio of A. sacrorum and the total phosphorus of root were negatively correlated to corresponding soil indices. The correlation between shoot nutrition and soil was greater than that between soil and root nutrition. In conclusion, middle position of shady slope was optimal for the growth of A. sacrorum. The stoichiometric characteristics of plants were significantly correlated with soil nutrient condition. Aspect and slope position had a significant effect on the stoichiometric cha-racteristics of A. sacrorum community and soil. Proper A. sacrorum community could help restore soil nutrition.

[Population dynamics of Artemisia scoparia in heterogeneous habitats in the desert steppe]. / è’æ¼ è‰åŽŸå¼‚è´¨ç”Ÿå¢ƒä¸‹çŒªæ¯›è’¿ç§ç¾¤åŠ¨æ€.

To understand the intra- and inter-annual population dynamics of Artemisia scoparia in the desert steppe, we set up three treatments, i.e., increasing the precipitation by 30%, reducing the precipitation by 30%, and the control (CK) in each soil habitat of aeolian sandy soil, sierozem soil, and bedrock weathered sedimentary soil. We drew up the dynamic life table to produce population survival and death curves and analyzed the population dynamics of A. scoparia in different habitats. Results showed that the survival curve of A. scoparia was approached to Deevey-1type. The survival rate was high in the early growth stage and tended to be relatively stable. The mortality rate maintained at a low level, but rose fast at the end of the growth stage. The individual survival number of A. scoparia in all habitats fluctuated at the early stage and declined at the later stage. The mortality rates of A. scoparia in habitats of both aeolian sandy soil and sierozem soil fluctuated greatly. There was no significant difference in the effects of increased and decreased precipitation treatments on the mortality rate of A. scoparia. Soil types had significant effects on all parameters, including the plant height, crown width, density, cover, and biomass of A. scoparia. Precipitation treatments had significant impacts on plant height, crown width and coverage of A. scoparia, and had no significant effect on plant density and biomass. The interactions between soil type and precipitation treatments had only a significant impact on plant height and crown width. The plasticity index of biomass in the habitat of bedrock weathered sedimentary soil was significantly higher than that in habitats of aeolian sandy soil and sierozem soil, while the plasticity index of plant coverage in the habitats of both sierozem soil and bedrock weathered sedimentary soil were significantly higher than that in the habitat of aeolian sandy soil. The density plasticity index of increased precipitation treatment was significantly higher than those of CK and the decreased precipitation treatments. The plasticity index of plant height and crown width were higher than other parameters, indicating that A. scoparia could respond to habitat changes by giving priority to these two parameters under different habitat pressures.

Freezing resistance, safety margins, and survival vary among big sagebrush populations across the western United States.

PREMISE: Physiological responses to temperature extremes are considered strong drivers of species' demographic responses to climate variability. Plants are typically classified as either avoiders or tolerators in their freezing-resistance mechanism, but a gradient of physiological-threshold freezing responses may exist among individuals of a species. Moreover, adaptive significance of physiological freezing responses is poorly characterized, particularly under warming conditions that relax selection on cold hardiness. METHODS: Freezing responses were measured in winter and again for new foliage in spring for 14 populations of Artemisia tridentata collected throughout its range and planted in a warm common garden. The relationships of the freezing responses to survival were evaluated in the warm garden and in two colder gardens. RESULTS: Winter and spring freezing resistance were not correlated and appeared to be under differing selection regimes, as evident in correlations with different population climate of origin variables. All populations resisted considerably lower temperatures in winter than in spring, with populations from more continental climates showing narrower freezing safety margins (difference in temperatures at which ice-nucleation occurs and 50% reduction in chlorophyll fluorescence occurs) in spring. Populations with greater winter freezing resistance had lower survivorship in the warmest garden, while populations with greater spring freezing resistance had lower survivorship in a colder garden. CONCLUSIONS: These survivorship patterns relative to physiological thresholds suggest excess freezing resistance may incur a survival cost that likely relates to a trade-off between carbon gain and freezing resistance during critical periods of moisture availability. This cost has implications for seed moved from cooler to warmer environments and for plants growing in warming environments.

A comprehensive analysis of interseasonal and interannual energy and water balance dynamics in semiarid shrubland and forest ecosystems.

Accurate estimation of ecosystem-scale land surface energy and water balance has great importance in weather and climate studies. This paper summarizes seasonal and interannual fluctuations of energy and water balance components in two distinctive semiarid ecosystems, sagebrush (SB) and lodgepole pine (LP) in the Snake River basin of Idaho. This study includes 6 years (2011-2016) of eddy covariance (EC) along with modeled estimates. An analysis of the energy balance indicated a higher energy balance ratio (0.88) for SB than for LP (0.86). The inclusion of canopy storage (CS) increased the association between turbulent fluxes and available energy in LP. Green vegetation fraction (GVF) significantly controlled evapotranspiration (ET) and surface energy partitioning when available energy and soil moisture were not limited. Seasonal water balance in the Budyko framework showed severe water-limited conditions in SB (6-9 months) compared to LP (6-7 months). Based on the validated Noah land surface model estimates, direct soil evaporation (ESoil) is the main component of ET (62 to 79%) in SB due to a large proportion of bare soil (60%), whereas at the lodgepole pine site, it was transpiration (ETran, 42-52%). A complementary ratio (CR) analysis on ET and potential ET (PET) showed a strong asymmetric CR in SB, indicating significant advection. Both SG and LP showed strong coupling between soil moisture (SM) and air temperature (Ta). However, a weak coupling was observed in SB when the soil was dry and Ta was high. This weak coupling was due to the presence of net advection. The results presented here have a wider application: to help us understand and predict the survival, productivity, and hydroclimatology of water-limited ecosystems.

Arbuscular mycorrhizal symbiosis and achene mucilage have independent functions in seedling growth of a desert shrub.

Arbuscular mycorrhizal (AM) symbiosis can play a role in improving seedling establishment in deserts, and it has been suggested that achene mucilage facilitates seedling establishment in sandy deserts and that mucilage biodegradation products may improve seedling growth. We aimed to determine if AM symbiosis interacts with achene mucilage in regulating seedling growth in sand dunes. Up to 20 A M fungal taxa colonized Artemisia sphaerocephala roots in the field, and mycorrhizal frequency and colonization intensity exhibited seasonal dynamics. In the greenhouse, total biomass of AM fungal-colonized plants decreased, whereas the root/shoot ratio increased. AM symbiosis resulted in increased concentrations of nutrients and chlorophyll and decreased concentrations of salicylic acid (SA) and abscisic acid (ABA). Achene mucilage had a weaker effect on biomass and on nutrient, chlorophyll, and phytohormone concentration than did AM symbiosis. We suggest that AM symbiosis and achene mucilage act independently in enhancing seedling establishment in sandy deserts.

In vitro effects of Artemisia sieberi on Echinococcus granulosus protoscolices.

Hydatidosis is a parasitic zoonotic disease. Surgery is one of its treatment modalities during which protoscolices are likely to be released into the peritoneal cavity and cause recurrence of the disease. Given the above problem and the complications associated with conventional anti-parasitic agents, it is imperative to find an effective and natural protoscolicidal agent. The present study was conducted to evaluate effects of Artemisia sieberi on Echinococcus granulosus protoscolices. Protoscolices were collected from slaughtered livestock in Kerman abattoir and the effect of three concentrations of aqueous extract of A. sieberi (25 mg ml-1, 50 mg ml-1 and 75 mg ml-1) was assessed over three different exposure periods. Results showed that scolicidal effect of this extract at exposure periods of 2, 5 and 10 min was 76 ±â€¯1.4, 76.8 ±â€¯1.41 and 85.7 ±â€¯3.29 percent at concentration of 25 mg ml-1 and 76.8 ±â€¯1.4, 78 ±â€¯3.18 and 86.4 ±â€¯24.9 percent at concentration of 50 mg ml-1 and finally 80 ±â€¯2.73, 90 ±â€¯0.79 and 92.6 ±â€¯1.27 percent at concentration of 75 mg ml-1, respectively. It can be concluded that the aqueous extract of A. sieberi has a protoscolicidal activity and can be considered a natural agent against hydatid cyst protoscolices.

Preferences of Specialist and Generalist Mammalian Herbivores for Mixtures Versus Individual Plant Secondary Metabolites.

Herbivores that forage on chemically defended plants consume complex mixtures of plant secondary metabolites (PSMs). However, the mechanisms by which herbivores tolerate mixtures of PSMs are relatively poorly understood. As such, it remains difficult to predict how PSMs, singly or as complex mixtures, influence diet selection by herbivores. Although relative rates of detoxification of PSMs have been used to explain tolerance of PSMs by dietary specialist herbivores, few studies have used the rate of detoxification of individual PSMs to understand dietary preferences of individual herbivores for individual versus mixtures of PSMs. We coupled in vivo experiments using captive feeding trials with in vitro experiments using enzymatic detoxification assays to evaluate the dietary preferences and detoxification capacities of pygmy rabbits (Brachylagus idahoensis), dietary specialists on sagebrush (Artemisia spp.), and mountain cottontails (Sylvilagus nuttallii), dietary generalists. We compared preference for five single PSMs in sagebrush compared to a mixture containing those same five PSMs. We hypothesized that relative preference for individual PSMs would coincide with faster detoxification capacity for those PSMs by specialists and generalists. Pygmy rabbits generally showed little preference among individual PSMs compared to mixed PSMs, whereas mountain cottontails exhibited stronger preferences. Pygmy rabbits had faster detoxification capacities for all PSMs and consumed higher concentrations of individual PSMs versus a mixture than cottontails. However, detoxification capacity for an individual PSM did not generally coincide with preferences or avoidance of individual PSMs by either species. Cottontails avoided, but pygmy rabbits preferred, camphor, the PSM with the slowest detoxification rate by both species. Both species avoided ß-pinene despite it having one of the fastest detoxification rate. Taken together our in vivo and in vitro results add to existing evidence that detoxification capacity is higher in dietary specialist than generalist herbivores. However, results also suggest that alternative mechanisms such as absorption and the pharmacological action of individual or mixtures of PSMs may play a role in determining preference of PSMs within herbivore species.

Climate-based seed transfer of a widespread shrub: population shifts, restoration strategies, and the trailing edge.

Genetic resources have to be managed appropriately to mitigate the impact of climate change. For many wildland plants, conservation will require knowledge of the climatic factors affecting intraspecific genetic variation to minimize maladaptation. Knowledge of the interaction between traits and climate can focus management resources on vulnerable populations, provide guidance for seed transfer, and enhance fitness and resilience under changing climates. In this study, traits of big sagebrush (Artemisia tridentata) were examined among common gardens located in different climates. We focus on two subspecies, wyomingensis and tridentata, that occupy the most imperiled warm-dry spectrum of the sagebrush biome. Populations collected across the sagebrush biome were recorded for flower phenology and survival. Mixed-effects models examined each trait to evaluate genetic variation, environmental effects, and adaptive breadth of populations. Climate variables derived from population-source locations were significantly associated with these traits (P < 0.0001), explaining 31% and 11% of the flower phenology and survival variation, respectively. To illustrate our model and assess variability in prediction, we examine fixed and focal point seed transfer approaches to map contemporary and climate model ensemble projections in two different regions of the sagebrush biome. A comparison of seed transfer areas predicts that populations from warmer climates become more prevalent, replacing colder-adapted populations by mid-century. However, these warm-adapted populations are often located along the trailing edge, margins of the species range predicted to be lost due to a contraction of the climatic niche. Management efforts should focus on the collection and conservation of vulnerable populations and prudent seed transfer to colder regions where these populations are projected to occur by mid-century. Our models provide the foundation to develop an empirical, climate-based seed transfer system for current and future restoration of big sagebrush.

Grazing effects on the nutritive value of dominant species in steppe grasslands of northern China.

BACKGROUND: Forage nutritive value plays an important role in livestock nutrition and maintaining sustainable grassland ecosystems, and grazing management can affect the quality of forage. In this study, we investigated the effects of different grazing intensities on the nutritive values of Leymus chinensis (Trin.) Tzvelev, Artemisia spp. and Carex duriuscula C. A. Mey in the steppes of China during the growing seasons from 2011 to 2013. Five grazing management treatments were implemented: (1) rest grazing in spring, heavy grazing in summer and moderate grazing in autumn (RHM), (2) rest grazing in spring, moderate grazing in summer and heavy grazing in autumn (RMH), (3) heavy grazing though all seasons (HHH), (4) heavy grazing in spring and summer and moderate grazing in autumn (HHM) and (5) continuous moderate grazing in all seasons (MMM). RESULTS: There were significant effects of year, season, treatment, and year × season and year × treatment interactions only on the crude protein of L. chinensis (P < 0.05). The crude protein concentrations of L. chinensis in the plots of constant high grazing pressure (HHH) and reduced grazing pressure in the last grazing stage (HHM) were higher than with deferred grazing (RMH and RHM, P < 0.05) in spring from 2011 to 2012. For Artemisia spp. and C. duriuscula, the crude protein concentration in HHH was higher than that in RMH (P < 0.05) in the summer of 2011. There were no significant differences (P > 0.05) for ether extract, neutral detergent fiber, acid detergent fiber and Ca concentration for any of the grasses in spring and summer from 2011 to 2013 under the different grazing management treatments. CONCLUSIONS: The nutritive value of L. chinensis was more responsive to grazing disturbance than Artemisia spp. and C. duriuscula, and heavy grazing maintained a relatively high crude protein content in all species. Seasonal and interannual seasonal differences in grazing management combinations were two of the most important factors in determining the variability of forage nutritive value, including crude protein, ether extract, neutral detergent fiber, acid detergent fiber and calcium, for L. chinensis, Artemisia spp. and C. duriuscula. We suggest that moderate grazing should be adopted to ensure the quality and yield of forage and promote the sustainable development of animal husbandry.

Shrub range expansion alters diversity and distribution of soil fungal communities across an alpine elevation gradient.

Global climate and land use change are altering plant and soil microbial communities worldwide, particularly in arctic and alpine biomes where warming is accelerated. The widespread expansion of woody shrubs into historically herbaceous alpine plant zones is likely to interact with climate to affect soil microbial community structure and function; however, our understanding of alpine soil ecology remains limited. This study aimed to (i) determine whether the diversity and community composition of soil fungi vary across elevation gradients and to (ii) assess the impact of woody shrub expansion on these patterns. In the White Mountains of California, sagebrush (Artemisia rothrockii) shrubs have been expanding upwards into alpine areas since 1960. In this study, we combined observational field data with a manipulative shrub removal experiment along an elevation transect of alpine shrub expansion. We utilized next-generation sequencing of the ITS1 region for fungi and joint distribution modelling to tease apart effects of the environment and intracommunity interactions on soil fungi. We found that soil fungal diversity declines and community composition changes with increasing elevation. Both abiotic factors (primarily soil moisture and soil organic C) and woody sagebrush range expansion had significant effects on these patterns. However, fungal diversity and relative abundance had high spatial variation, overwhelming the predictive power of vegetation type, elevation and abiotic soil conditions at the landscape scale. Finally, we observed positive and negative associations among fungal taxa which may be important in structuring community responses to global change.

Multi-model comparison highlights consistency in predicted effect of warming on a semi-arid shrub.

A number of modeling approaches have been developed to predict the impacts of climate change on species distributions, performance, and abundance. The stronger the agreement from models that represent different processes and are based on distinct and independent sources of information, the greater the confidence we can have in their predictions. Evaluating the level of confidence is particularly important when predictions are used to guide conservation or restoration decisions. We used a multi-model approach to predict climate change impacts on big sagebrush (Artemisia tridentata), the dominant plant species on roughly 43 million hectares in the western United States and a key resource for many endemic wildlife species. To evaluate the climate sensitivity of A. tridentata, we developed four predictive models, two based on empirically derived spatial and temporal relationships, and two that applied mechanistic approaches to simulate sagebrush recruitment and growth. This approach enabled us to produce an aggregate index of climate change vulnerability and uncertainty based on the level of agreement between models. Despite large differences in model structure, predictions of sagebrush response to climate change were largely consistent. Performance, as measured by change in cover, growth, or recruitment, was predicted to decrease at the warmest sites, but increase throughout the cooler portions of sagebrush's range. A sensitivity analysis indicated that sagebrush performance responds more strongly to changes in temperature than precipitation. Most of the uncertainty in model predictions reflected variation among the ecological models, raising questions about the reliability of forecasts based on a single modeling approach. Our results highlight the value of a multi-model approach in forecasting climate change impacts and uncertainties and should help land managers to maximize the value of conservation investments.

A warmer and drier climate in the northern sagebrush biome does not promote cheatgrass invasion or change its response to fire.

Dryland shrub communities have been degraded by a range of disturbances and now face additional stress from global climate change. The spring/summer growing season of the North American sagebrush biome is projected to become warmer and drier, which is expected to facilitate the expansion of the invasive annual grass Bromus tectorum (cheatgrass) and alter its response to fire in the northern extent of the biome. We tested these predictions with a factorial experiment with two levels of burning (spring burn and none) and three climate treatments (warming, warming + drying, and control) that was repeated over 3 years in a Montana sagebrush steppe. We expected the climate treatments to make B. tectorum more competitive with the native perennial grass community, especially Pseudoroegneria spicata, and alter its response to fire. Experimental warming and warming + drying reduced B. tectorum cover, biomass, and fecundity, but there was no response to fire except for fecundity, which increased; the native grass community was the most significant factor that affected B. tectorum metrics. The experimental climate treatments also negatively affected P. spicata, total native grass cover, and community biodiversity, while fire negatively affected total native grass cover, particularly when climate conditions were warmer and drier. Our short-term results indicate that without sufficient antecedent moisture and a significant disruption to the native perennial grass community, a change in climate to a warmer and drier spring/summer growing season in the northern sagebrush biome will not facilitate B. tectorum invasion or alter its response to fire.

Seasonal variation in water uptake patterns of three plant species based on stable isotopes in the semi-arid Loess Plateau.

Water is a limiting factor and significant driving force for ecosystem processes in arid and semi-arid areas. Knowledge of plant water uptake pattern is indispensable for understanding soil-plant interactions and species coexistence. The 'Grain for Green' project that started in 1999 in the Loess Plateau of China has led to large scale vegetation change. However, little is known about the water uptake patterns of the main plant species that inhabit in this region. In this study, the seasonal variations in water uptake patterns of three representative plant species, Stipa bungeana, Artemisia gmelinii and Vitex negundo, that are widely distributed in the semi-arid area of the Loess Plateau, were identified by using dual stable isotopes of δ2H and δ18O in plant and soil water coupled with a Bayesian mixing model MixSIAR. The soil water at the 0-120cm depth contributed 79.54±6.05% and 79.94±8.81% of the total water uptake of S. bungeana and A. gmelinii, respectively, in the growing season. The 0-40cm soil contributed the most water in July (74.20±15.20%), and the largest proportion of water (33.10±15.20%) was derived from 120-300cm soils in August for A. gmelinii. However, V. negundo obtained water predominantly from surface soil horizons (0-40cm) and then switched to deep soil layers (120-300cm) as the season progressed. This suggested that V. negundo has a greater degree of ecological plasticity as it could explore water sources from deeper soils as the water stress increased. This capacity can mainly be attributed to its functionally dimorphic root system. V. negundo may have a competitive advantage when encountering short-term drought. The ecological plasticity of plant water use needs to be considered in plant species selection and ecological management and restoration of the arid and semi-arid ecosystems in the Loess Plateau.

Effects of foliage litter of a pioneer shrub (Artemisia halodendron) on germination from the soil seedbank in a semi-arid sandy grassland in China.

Vegetation recovery during succession is an important process for ecological restoration of the soil, especially in degraded sandy land. However, the driving mechanisms, such as how a pioneer species competes with other species, is uncertain. In China's Horqin Sandy Land, Artemisia halodendron is an important shrub that is common on semi-fixed dunes, where it replaces Agriophyllum squarrosum during succession, and is an important indicator species of the second stage of dune stabilization. However, how it outcompetes other species is still unclear. In this study, we conducted a seed bank germination experiment using soil from the native habitats of A. halodendron on semi-fixed dunes. We covered the soil with foliage litter of A. halodendron at a range of concentrations. Seed germination and seedling growth were strongly affected by the foliage litter. Seed germination and seedling growth were not harmed by a low concentration (≤50 g m-2) of the foliage litter but severely inhibited by high concentrations (≥100 g m-2). Strong allelopathy, indicated by decreased germination, increased seedling loss, and decreased plant biomass, appeared during the later stages of germination (after about 20 days of incubation). Our results suggest that as a pioneer shrub during the vegetation succession that occurs during dune stabilization, A. halodendron outcompeted other species through the allelopathic effect of its foliage litter. This helps to explain the patchy distribution and heterogeneity of vegetation communities in the Horqin Sandy Land.

Precipitation affects plant communication and defense.

Anti-herbivore defense shows high levels of both inter- and intraspecific variability. Defending against herbivores may be costly to the plant when it requires a tradeoff in allocation between defense and other missed opportunities, such as reproduction. Indeed, the plastic expression of defensive traits allows the plant to invest resources in defense only when the risk of being damaged actually increases, avoiding wasted resources. Plants may assess risk by responding to volatile cues emitted by neighbors that are under attack. Most plastic responses likely depend on environmental conditions. In this experiment, we investigated the effect of water availability on resistance induced by volatile cues in sagebrush. We found that plants receiving additional water over summer and/or volatile cues from neighbor donor plants showed reduced herbivore damage compared to control plants. Interestingly, we found no evidence of interactions between additional water and volatile cues. We performed an inferential analysis comparing historical records of the levels of herbivore damage during different years that had different temperature and precipitation accumulations. Results confirmed findings from the experiment, as the regression model indicated that sagebrush was better defended during wetter and hotter seasons. Reports from the literature indicated that sagebrush is extremely sensitive to water availability in the soil. We suggest that water availability may directly affect resistance of herbivory as well as sensitivity to cues of damage. Costs and benefits of allocating resources to defensive traits may vary with environmental conditions.